There are others that have been integrated directly into the builds of Blender, but those (linked to) versions give you the choice of rendering internal (blender view-port) or external (Lux GUI). There is a short vid (on the download page) on how to add the plugin. (you must use Blender 2.63a for that plugin, currently:- http://www.blender.org/download/get-blender/ )